JPH07167698A - Coriolis flowmeter - Google Patents

Abstract

PURPOSE:To detect a time difference signal proportional to a Coriolis force as an average stable signal with less noise influence without using a clock. CONSTITUTION:A first vibration signal displacement-detected at symmetrical two positions of a measuring tube is formed as a fundamental sine wave of vibration by a first integrator 3, converted to an arc sine wave having a predetermined amplitude by a first converter 15 to a triangular wave having a predetermined amplitude by a first AGC circuit 7. Similar waveform conversion is conducted for a second vibration signal, subtracted by a subtracter 9, and a phase difference signal phi is detected as a height phi of a trapezoidal signal. A period of a vibration signal obtained by a period measuring circuit 10 is multiplied by the difference phip to output a time difference DELTAT.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis flowmeter, and more particularly to a Coriolis flowmeter for obtaining a Coriolis force acting on a measuring tube as a time difference signal of a detection signal at a vibration detecting position of the measuring tube.

[0002]

2. Description of the Related Art When a measuring tube is supported at both ends and the central portion of the supported measuring tube is driven alternately in a direction perpendicular to the axis,
When the fluid moves, a phase difference occurs between the inflow side and the outflow side of the measuring tube with the center of the measuring tube as the center. This phase difference is
A Coriolis flow meter that is based on Coriolis force and has a value proportional to the mass flow rate and that measures the mass flow rate by detecting the phase difference is well known. Thus, the detection of the phase difference is
The measurement is performed by measuring the time difference when the measuring tube at the detection position passes through the reference plane, with the plane passing through the tube axis of the measuring tube in the stationary state of the measuring tube as the reference plane. Specifically, the time difference is obtained by shaping the signals of the displacement detectors of the measuring pipes, which are mounted at symmetrical positions on the inflow side and the outflow side of the measuring pipe, into square waves, and starting up each shaped square wave. It is calculated from the number of constant frequency clocks counted during the time difference.

[0003]

As described above, the Coriolis flowmeter supports the measuring tube at two points and applies vibration around the supporting point to the supported measuring tube with the supporting point as a node, and It is a mass flow meter that detects the Coriolis force acting on the fluid flowing through the measuring tube. However, the phase difference signal of the measuring tube generated at a predetermined symmetrical position on the inflow side and the outlet side of the measuring tube due to the Coriolis force is an extremely small amount as compared with the drive amplitude of the measuring tube. Therefore, the time difference detected in proportion to the phase difference signal is also extremely small. In order to measure this time difference with high resolution, it is necessary to increase the clock frequency. However, since the Coriolis flowmeter is mounted between the upstream and downstream pipes, it is easily affected by external vibrations and noise due to the pipes, and stable time difference measurement is not possible simply by using a clock with high resolution.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a Coriolis flowmeter having a time difference detecting means capable of obtaining an averaged and stable time difference with less noise influence without using a clock for measuring the time difference. It is what

[0005]

In order to solve the above-mentioned problems, the present invention provides (1) a measuring pipe through which a fluid flows, and a supporting member for supporting the measuring pipe at two points in the flow direction with a space therebetween. ,
Driving means for driving the measuring tube around the supporting member, and a position symmetrical between the supporting members of the measuring tube,
A first detector and a second detector for detecting the vibration of the measuring tube, and a time on a reference time axis is detected from the vibration signals detected by the first detector and the second detector, and is proportional to the time difference. In a Coriolis flowmeter having a time difference detecting means for obtaining a mass flow rate, the time difference detecting means shapes the vibration signal detected by the first detector into a sine wave signal, and the shaped sine wave signal is an inverse sine wave. A first conversion circuit for converting the signal into a signal, a second conversion circuit for shaping the vibration signal detected by the second detector into a sine wave signal, and converting the shaped sine wave signal into an inverse sine wave signal; A first amplitude control circuit for controlling the amplitude of the inverse sine wave signal output from the first conversion circuit to a constant value, and an amplitude of the inverse sine wave signal output from the second conversion circuit for the first amplitude control circuit. Said inverse sine wave signal controlled by Second controlling the equal amplitude amplitude
An amplitude control circuit, a subtraction circuit for subtracting the outputs of the first amplitude control circuit and the second amplitude control circuit, a cycle measuring circuit for measuring the cycle of the vibration signal, and a cycle of the measured vibration signal. And a multiplication circuit that multiplies the output of the subtraction circuit, and obtains the time difference from the output of the multiplication circuit, or (2) In (1), the first conversion circuit is used in the time difference detection means. A waveform conversion circuit that outputs a triangular wave signal having the same phase as the first vibration signal and outputs the second conversion circuit as a triangular wave signal having the same phase as the second vibration signal, or (3) the above (1) or ( In 2), in the time difference detection means, the triangular wave signal whose amplitude is controlled by the first amplitude control circuit and the second vibration control circuit is clipped with a voltage smaller than the triangular wave signal peak voltage, Is characterized in that the output as square wave signal.

[0006]

The sine wave signals which are displacement-detected at symmetrical positions from the supporting positions on the inlet side and the outlet side of the measuring pipe are converted into inverse sine wave signals to have a phase difference of ± (π / 2. ) As a peak value, input it to the subtraction circuit, calculate the phase difference from the subtraction value, multiply this by the period of the detected sine wave of the vibration signal, and obtain the time difference proportional to the Coriolis force. Ask.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the Coriolis flowmeter according to the present invention, the structure of a basic Coriolis flowmeter will be described first. FIG. 4 is a basic structural diagram for explaining the Coriolis flowmeter according to the present invention, in which 20 is a Coriolis flowmeter main body, 2
1 is a base, 22 is a measuring tube, 23 and 24 are support members, 25
Is a driving means, 26 is a first detector, and 27 is a second detector.

The Coriolis flowmeter main body 20 has a measurement tube 22 through which a fluid flows, and a first support member 23 fixed to a base 21 that supports the measurement tube 22 at two points separated by an interval L in the flow direction.
The second support member 24, the driving means 25 for driving the measuring tube 22 in the direction perpendicular to the axis OO at the center of the supported measuring tube 22, and the measuring tube 22 driven by the driving means 25 by Coriolis force. Detectors 26, 2 for detecting the phase displacement occurring in the
It consists of 7.

The driving means 25 comprises, for example, a magnetic body 25a fixed to the measuring tube 22 and a coil 25b fixed to the base 21 so as to face the magnetic body 25a.
By applying a driving current of a sine wave to the measuring tube 22
Are driven in the directions of the arrows ± ω ₁ , ω ₂ around the supporting members 23, 24.

The detectors 26 and 27 are magnets 26a and 27a of the same standard having the same principle structure and the detection coil 26.
b and 27b, and the magnets 26a and 27a are the measuring tubes 2
The detection coils 26b and 27b are fixed to the base 21 at symmetrical positions from the two inlets and outlets.

Coriolis flowmeter main body 2 having the above structure
When 0 is driven by the driving means 25 with a sine wave, the detector 2
At 6 and 27, a sine wave signal having a minute phase difference due to the Coriolis force acting on the measuring tube 22 is detected. When the fluid is flowing in the direction of the arrow Q, the measuring tube 22 is + ω ₁ ,
When driven in the −ω ₂ direction, the sine wave signal of the first detector 26 has a phase delay proportional to the Coriolis force with respect to the sine wave signal of the second detector 27. On the contrary, −ω ₁ , −
When driven in the ω ₂ direction, the phase lag is opposite.

The present invention detects the phase delay, that is, the phase difference φ as the time difference ΔT, and the principle thereof will be described. The sine wave signal output from the first detector 26 is y ₁ , and the sine wave signal output from the second detector 27 is y ₂
Then, y ₁ = A ₁ sin ωt (1) y ₂ = A ₁ sin (ωt + φ) (2) where A ₁ and A ₂ are amplitudes, ω is a driving angular velocity, and t is time.

When the expressions (1) and (2) are respectively divided by the amplitude, sin ωt = y ₁ / A ₁ (3) sin (ωt + φ) = y ₂ / A ₂ (4) Expressions (3) and (4) Taking the inverse sine function of, sin ⁻¹ (sin ωt) = sin ⁻¹ (y ₁ / A ₁ ) = ωt (5) sin [sin (ω + φ)] = sin ⁻¹ (y ₂ / A ₂ ) = ωt + φ (6)

From equations (5) and (6), φ = sin ^-1 (y ₂ / A ₂ ) -sin ^-1 (y ₁ / A ₁ ) (7) Here, when the frequency of the output signal is f, Since the time difference ΔT is ΔT = (φ / 2π) × (1 / f) (8), from (7) and (8), if the period 1 / f = t _f , then ΔT = (1 / 2π) × {Sin ⁻¹ (y ₂ / A ₂ ) −sin ⁻¹ (y ₁ / A ₁ )} × t _f (9), and the time difference ΔT can be calculated.

FIG. 1 is a block diagram for explaining an example of the time difference detecting means according to the present invention, in which 1 is a first.
Vibration signal input terminal, 2 is second vibration signal input terminal, 3 is first integration circuit, 4 is second integration circuit, 5 is first conversion circuit, 6
Is a second conversion circuit, 7 is a first amplitude control (AGC) circuit, and 8 is
Is a second amplitude control (AGC) circuit, 9 is a subtraction circuit, 10 is a period measuring circuit, and 12 is an output terminal, which is a block circuit for implementing the above equation (9).

The first integrating circuit 3 and the second integrating circuit 4 are the same circuit, and both remove noise and harmonic components contained in the vibration signal of the detector and shape the waveform into a sine wave. The first conversion circuit 5 and the second conversion circuit 6 are also the same circuits, both of which are circuits for converting the waveform-shaped sine wave vibration signal into an inverse sine wave signal. The first AGC circuit 7 and the second AGC circuit 8 have the same circuit configuration, and both control the amplitude values of the first and second inverse sine wave signals to the same amplitude value.

The first vibration signal input terminal 1, the first integration circuit 3, the first conversion circuit 5, and the first AGC circuit 7 are connected in series, and the second vibration signal input terminal 2 side similarly has the second integration circuit 4, The second conversion circuit 6 and the second AGC circuit 8 are connected in series, the first AGC circuit 7 and the second AGC circuit 8 are connected to the subtraction circuit 9, and the subtraction circuit 9 is connected to one input end of the multiplication circuit 11. . On the other hand, the second inverse sine wave signal of the second conversion circuit 6 is connected to the cycle measuring circuit 10 and connected to the other input terminal of the multiplying circuit 11 for a cycle having the same cycle as the measured vibration signal to obtain the phase difference signal φ. It is multiplied by the period t _f and output from the output terminal 12.

The time difference measuring means of FIG. 1 having the above construction will be described with reference to Table 1 and FIG. Table 1 shows the relationship between the sine wave and the inverse sine wave with respect to the phase of the vibration signal, and FIG.
It is a waveform diagram explaining the principle of phase difference detection. The vibration signal input from the first vibration signal input terminal 1 is waveform-shaped by the first integration circuit 3 and becomes a sinx periodic signal shown in FIG. 2 (1). The sine wave sinx is a periodic function that has peak values at 2 / 4π and 6 / 4π and zero-crosses at a phase that is an integral multiple of π. In addition, sin ^-1 (sin which is the inverse function of sine wave sinx
x) has peak values ± π / 2 at 2π / 4 and 6 / 4π,
It becomes a triangular wave signal that zero-crosses at the position of an integral multiple of π.

[0019]

[Table 1]

On the other hand, the vibration signal input from the second vibration signal input terminal 2 has a phase difference φ with the vibration signal of the first detector 1, and the phase difference φ is as shown in FIG. Is represented on the vertical axis. Therefore, the inverse sine wave sin ⁻¹ (sinx + φ) has a phase difference φ and becomes the same triangular wave signal as sin ⁻¹ (sin x).

FIG. 2 (4) shows sin ^-1 (sinx) of FIG. 2 (2).
2 (3) and sin ⁻¹ {sin (x + φ)} are subtracted by the subtraction circuit 9 to obtain a trapezoidal periodic function that zero-crosses at a phase of an integer multiple of approximately π / 2. Is 2φ and the fall time delay is Δt, and the height of the trapezoid changes in proportion to the phase difference φ. In this way, the phase difference signal φ is detected as the phase difference signal φ having a constant height during the time when the phase is approximately π, and thus the averaged phase difference φ is detected. Therefore, the phase difference signal φ is multiplied by the period t _f. The time difference signal ΔT proportional to the obtained Coriolis force is also averaged, and the time difference signal having no noise influence is detected.

As is clear from the above description, the sine wave si
nx and the inverse sine wave sin ^-1 (sinx) are periodic functions of the same period, and the inverse sine wave sin ^-1 (sinx) is a triangular wave, so a sine wave
Even if sinx is directly converted into a triangular wave, the same trapezoidal phase difference signal can be detected. That is, the first and second conversion circuits 5 and 6 are waveform conversion circuits for converting a sine wave into a triangular wave having the same period, and the other circuits are configured in exactly the same way as the circuit shown in FIG. ΔT is obtained. Further, as shown in FIG. 3, the phase difference φ can be similarly detected by a trapezoidal wave obtained by clipping the top of the triangular wave with a constant voltage.

FIG. 3 shows the time difference measuring means according to the present invention.
FIG. 6 is a waveform diagram for explaining another embodiment, and FIG.
Is a trapezoidal wave by clipping the top of the inverse sine wave sin ^-1 (sinx) whose peak value is controlled to be constant by the AGC circuits 7 and 8 at a constant voltage, for example, ± V at a constant voltage. 3 (2) is the inverse sine wave sin ⁻¹ {sin (x + φ)}.
The top of is clipped with a constant voltage ± V, and the phase difference φ
Becomes a trapezoidal signal of height ± φ which becomes 0 near the clipped time as shown in FIG. 3C, and the same effect as the circuit of FIG. 1 can be obtained. In the above description, the straight measuring tube shown in FIG. 4 is described, but the measuring tube does not have to be a straight tube, and the same time difference detection can be applied to a curved tube.

[0024]

As is apparent from the above description, the present invention has the following effects. (1) It is not necessary to use a clock because a time difference proportional to the Coriolis force is detected. (2) Since the phase difference signal is represented by the height of the trapezoidal wave, a constant height is obtained for each half cycle of vibration, and an averaged value is obtained for the time difference signal obtained by multiplying the phase difference and the period. To be (3) Further, since the height of the trapezoidal wave is constant, it is less susceptible to noise.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an example of a time difference detection means according to the present invention.

FIG. 2 is a waveform diagram illustrating the principle of phase difference detection.

FIG. 3 is a waveform diagram for explaining another embodiment of the time difference measuring means according to the present invention.

FIG. 4 is a basic structural diagram for explaining a Coriolis flowmeter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st vibration signal input terminal, 2nd ... 2nd vibration signal input terminal, 3 ... 1st integrating circuit, 4 ... 2nd integrating circuit, 5 ... 1st converting circuit, 6 ... 2nd converting circuit, 7 ... 1st Amplitude control (AG
C) circuit, 8 ... Second amplitude control (AGC) circuit, 9 ... Subtraction circuit, 10 ... Period measuring circuit, 12 ... Output terminal, 20 ... Coriolis flowmeter main body, 21 ... Base, 22 ... Measuring tube, 23,
24 ... Support member, 25 ... Driving means, 26 ... First detector,
27 ... Second detector.

Claims (3)

[Claims] 1. A measuring tube through which a fluid flows, a support member for supporting the measuring tube at two points spaced apart in the flow direction, driving means for driving the measuring tube around the supporting member, and the measuring tube. A first detector and a second detector for detecting the vibration of the measuring tube at positions symmetrical between the supporting members, and a vibration signal detected by the first detector and the second detector on a reference time axis. In the Coriolis flowmeter having a time difference detecting means for detecting the time of, and obtaining a mass flow rate in proportion to the time difference, the time difference detecting means shapes the vibration signal detected by the first detector into a sine wave signal, A first conversion circuit for converting the shaped sine wave signal into an inverse sine wave signal, and the vibration signal detected by the second detector is shaped into a sine wave signal, and the shaped sine wave signal is inverse sine wave signal. A second conversion circuit for converting to A first amplitude control circuit for controlling the amplitude of the inverse sine wave signal output from the first conversion circuit to a constant value, and an amplitude of the inverse sine wave signal output from the second conversion circuit for the first amplitude control circuit. A second amplitude control circuit that controls the amplitude to be equal to the amplitude of the inverse sine wave signal controlled by a circuit; a subtraction circuit that subtracts the outputs of the first amplitude control circuit and the second amplitude control circuit; A cycle measuring circuit for measuring the cycle of the vibration signal, and a multiplication circuit for multiplying the cycle of the measured vibration signal by the output of the subtraction circuit, and the time difference is obtained from the output of the multiplication circuit. Coriolis flow meter. 2. A waveform converter for outputting, in the time difference detection means, a first conversion circuit as a triangular wave signal having the same phase as the first vibration signal and a second conversion circuit as a triangular wave signal having the same phase as the second vibration signal. The Coriolis flowmeter according to claim 1, which is a circuit. 3. The trapezoidal wave signal is obtained by clipping the triangular wave signal controlled to have a constant amplitude by the first amplitude control circuit and the second vibration control circuit with a voltage smaller than the peak voltage of the triangular wave signal in the time difference detection means. The Coriolis flowmeter according to claim 1, wherein the Coriolis flowmeter outputs.